Dejimon11

somari maker

Fighting game or an actual platformer 

a chair

We already got a fighting game it's called "Smash bros"

Platformer. Sonic and Mario are both platform games. I'd want to see Mario play through Sonic style levels and Sonic play through Mario style levels.

Smash Bros is a fighting game, but I honestly would prefer a more traditional fighting game with just the Mario and Sonic cast.

Cooking sim, obviously.

But in all seriousness, either a platformer, an RPG, or a racing game.

Something along the lines of "Goat Simulator."

Dating sim

A platformer crossover between 2 of the most recognizable characters in gaming history that made their names in that genre? That's ridiculous. Do you know how much effort that would take and how it would ruin their legacies if the two of them were to do that? 

@Forte why a racing game since we have Mario Kart and the Sonic all stars racing series? That would be redundant.

One benefit of a Mario & Sonic-specific fighting game is that it could (of course) have more characters from each series without annoying anyone who doesn't like to see one franchise get too many reps in Smash.

Anyway, I guess I'd like to see a platformer but I have no idea who the dev team would be since most of the dev teams I'd want to be involved are probably busy with other projects.

Spaghetti western. 

I was thinking of a racing game more akin to Sonic R.

A real party game with tons of fun mini-games. This Olympic stuff ain't it.

A racing game would be awesome too